In a conventional data-processing system, such as a computer and/or a computer network, one or more processors may communicate with input/output (I/O) devices over one or more buses. The I/O devices may be coupled to the processors through an I/O interface such as an I/O bridge, which can manage the transfer of information between a peripheral bus connected to the I/O devices and a shared bus connected to the processors. Additionally, the I/O interface may manage the transfer of information between system memory and the I/O devices or the system memory and the processors.
An I/O interface can also be utilized to transfer information between I/O devices and main storage components of a host processor. An I/O channel, for example, may connect the host directly to a mass storage device (e.g., disk or tape drive). In the case of a mainframe host processor, the channel is usually coupled to one or more device controllers. Each device controller can in turn be connected to a plurality of mass storage devices.
Small Computer Systems Interface (“SCSI”) is a set of American National Standards Institute (“ANSI”) standard electronic interface specification that allows, for example, computers to communicate with peripheral hardware. Common SCSI compatible peripheral devices may include: disk drives, tape drives, Compact Disc-Read Only Memory (“CD-ROM”) drives, printers and scanners. SCSI as originally created included both a command/response data structure specification and an interface and protocol standard for a parallel bus structure for attachment of devices. SCSI has evolved from exclusively parallel interfaces to include both parallel and serial interfaces. “SCSI” is now generally understood as referring either to the communication transport media (parallel bus structures and various serial transports) or to a plurality of primary commands common to most devices and command sets to meet the needs of specific device types as well as a variety of interface standards and protocols.
The collection of primary commands and other command sets may be used with SCSI parallel interfaces as well as with serial interfaces. The serial interface transport media standards that support SCSI command processing include: Fibre Channel, Serial Bus Protocol (used with the Institute of Electrical and Electronics Engineers 1394 FireWire physical protocol; “IEEE 1394”) and the Serial Storage Protocol (SSP).
SCSI interface transports and commands are also used to interconnect networks of storage devices with processing devices. For example, serial SCSI transport media and protocols such as Serial Attached SCSI (“SAS”) and Serial Advanced Technology Attachment (“SATA”) may be used in such networks. These applications are often referred to as storage networks. Those skilled in the art are familiar with SAS and SATA standards as well as other SCSI related specifications and standards. Information about such interfaces and commands is generally obtainable at the website http://www.t10.org.
Such SCSI storage networks are often used in large storage systems having a plurality of disk drives to store data for organizations and/or businesses. The network architecture allows storage devices to be physically dispersed in an enterprise while continuing to directly support SCSI commands directly. This architecture allows for distribution of the storage components in an enterprise without the need for added overhead in converting storage requests from SCSI commands into other network commands and then back into lower level SCSI storage related commands.
A SAS network typically comprises one or more SAS initiators coupled to one or more SAS targets via one or more SAS expander devices. In general, as is common in all SCSI communications, SAS initiators initiate communications with SAS targets. The expander devices expand the number of ports of a SAS network domain used to interconnect SAS initiators and SAS targets (collectively referred to as SAS devices)
One of the problems with current SAS expander devices is that there is minimal testing of SAS expanders in a complete domain aside from testing standard operations. A test is needed to stress the error handling capabilities of the expander itself. It is difficult to test the initiator's link error handling capabilities in an SAS domain when there are expanders present. Because SAS is a relatively new protocol, there are few tests which stress these characteristics. Many of the existing tests, such as stress tests, simply test the ability of an expander to exist in the domain under normal operation. Existing software tests do not test the ability of the SAS expander to recover from repeated severe errors, which are induced in the expander. Such tests also do not test the initiator's ability to handle these errors correctly. Such conditions, however, can occur and should be tested. Current testing techniques require additional hardware to test the domain and are also limited to testing no more than four links at a time, while an SAS domain may possess many more.